The Relative Contribution of Point Mutations and Genomic Rearrangements in BRCA1 and BRCA2 in High-Risk Breast Cancer Families

¹ Divisions of ¹Medical Genetics and ²Hematology-Oncology, Department of Medicine, ³Abramson Cancer Center, ⁴Department of Biostatistics and Epidemiology, and ⁵Joan Karnell Cancer Center at Pennsylvania Hospital, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania

^* To whom correspondence should be addressed. E-mail: knathans{at}mail.med.upenn.edu.

	Abstract

The demand for BRCA1 and BRCA2 mutation screening is increasing as their identification will affect medical management. However, both the contribution of different mutation types in BRCA1 and BRCA2 and whom should be offered testing for large genomic rearrangements have not been well established in the U.S. high-risk population. We define the prevalence and spectrum of point mutations and genomic rearrangements in BRCA genes in a large U.S. high-risk clinic population of both non-Ashkenazi and Ashkenazi Jewish descent, using a sample set representative of the U.S. genetic testing population. Two hundred fifty-one probands ascertained through the University of Pennsylvania high-risk clinic, all with commercial testing for BRCA1 and BRCA2, with an estimated prevalence of BRCA mutation 10% using the Myriad II model and a DNA sample available, were studied. Individuals without deleterious point mutations were screened for genomic rearrangements in BRCA1 and BRCA2. In the 136 non-Ashkenazi Jewish probands, 36 (26%) BRCA point mutations and 8 (6%) genomic rearrangements (7 in BRCA1 and 1 in BRCA2) were identified. Forty-seven of the 115 (40%) Ashkenazi Jewish probands had point mutations; no genomic rearrangements were identified in the group without mutations. In the non-Ashkenazi Jewish probands, genomic rearrangements constituted 18% of all identified BRCA mutations; estimated mutation prevalence (Myriad II model) was not predictive of their presence. Whereas these findings should be confirmed in larger sample sets, our data suggest that genomic rearrangement testing be considered in all non-Ashkenazi Jewish women with an estimated mutation prevalence 10%. [Cancer Res 2008;68(17):7006–14]

Key Words: BRCA1, BRCA2, point mutations, genomic rearrangements, U.S. clinic population

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